Method of designing electroluminescent device, electroluminescent device manufactured with the design method, and method of manufacturing electroluminescent device with the design method

ABSTRACT

A method of designing an electroluminescent device allows more accurate computation of an external emission spectrum output to the outside in a current injection state and accurate estimate of a quantity and/or a color of light extracted to the outside, an electroluminescent device manufactured with the design method, and a method of manufacturing an electroluminescent device with the design method.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a 371 of PCT/JP2015/065844 filed on Jun. 2, 2015which, in turn, claimed the priority of Japanese Patent Application No.2014-127360 filed on Jun. 20, 2014, both applications are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a method of designing anelectroluminescent device, an electroluminescent device manufacturedwith the design method, and a method of manufacturing anelectroluminescent device with the design method.

BACKGROUND ART

A surface emitting device high in luminous efficiency which includes anelectroluminescent device such as a light-emitting diode (LED) ororganic EL has recently attracted attention. The electroluminescentdevice is formed from an emissive layer lying between a planar cathodeand a planar anode, and generally in many cases, it is formed from atransparent electrode as an anode and a metal reflective electrode as acathode.

When the cathode is formed from a metal electrode, light is extractedfrom a side of the transparent anode, and the electroluminescent deviceis used as a single-emission light emitting device. When electrodes onopposing sides are formed from transparent electrodes, a transparentlight emitting device can be obtained and applications to decorativelighting are expected. Light emitted in an emissive layer is not totallyextracted. There are a substrate mode in which light is confined in atransparent base material, a waveguide mode in which light is confinedin an emissive layer or a transparent electrode, and a plasmon mode inwhich light is confined in a metal electrode, which are factors forrestriction of luminous efficiency of a device.

When an electroluminescent device is used for lighting or as adecorative light source, a color or a luminance of light which comesoutside is important. A color or a luminance of light extracted to theoutside, however, is varied due to interference with an opticalmulti-layer, and control thereof is disadvantageously difficult. It isimportant in applications to estimate a color or a luminance of lightextracted to the outside.

A computation method based on a photoluminescence spectrum of alight-emitting material is disclosed in Japanese Laid-Open PatentPublication No. 2010-147337 (PTD 1) and Japanese Laid-Open PatentPublication No. 2009-054382 (PTD 2) as a method of designing a colorcoordinate or a luminance of light which can be extracted to theoutside. A detailed method of computing light extraction efficiency isdisclosed in R. Meerheim et. al., Appl. Phys. Lett., 97, 253305 (2010)(NPD 1).

CITATION LIST Patent Document

-   PTD 1: Japanese Laid-Open Patent Publication No. 2010-147337-   PTD 2: Japanese Laid-Open Patent Publication No. 2009-054382

Non Patent Document

-   NPD 1: R. Meerheim et. al., Appl. Phys. Lett., 97, 253305 (2010)

SUMMARY OF INVENTION Technical Problem

In PTDs 1 and 2, however, an external spectrum is computed based on aphotoluminescence spectrum, and an electroluminescence spectrum in anactual current injection state of a device cannot accurately becomputed.

In NPD 1, a spectrum in an emissive layer should be assumed, however,NPD 1 is insufficient in detailed explanation as to how to set a ratiobetween electron injection and internal spectrum intensity and to set ashape of an internal spectrum so as to lessen an error betweenexperiments and computation or in explanation of a difference between aphotoluminescence spectrum and an electroluminescence spectrum, and adifference between experiments and computation has remained.

The present invention was made in view of the problems above, and thepresent invention provides a method of designing an electroluminescentdevice which allows more accurate computation of an external emissionspectrum output to the outside in a current injection state and accurateestimation of a quantity and/or a color of light extracted to theoutside, an electroluminescent device manufactured with the designmethod, and a method of manufacturing an electroluminescent device withthe design method.

Solution to Problem

A method of designing an electroluminescent device based on thisinvention is a method of designing an electroluminescent device havingan emissive layer between a first electrode and a second electrode, thefirst electrode and the second electrode being transparent electrodes,the emissive layer lying between a first functional layer and a secondfunctional layer, and the electroluminescent device having a firsttransparent member on a side of the first electrode opposite to a sidewhere the emissive layer is provided. A reference device including aconstruction of the electroluminescent device and a desired analyzeddevice including a construction of the electroluminescent device areprepared. Quantum optical analysis, electromagnetic field analysis, andray trace are performed with thicknesses and complex relativepermittivities of the first transparent member, the first electrode, thefirst functional layer, the second functional layer, the emissive layer,and the second electrode as well as a position of a light-emitting pointin the emissive layer and a distribution of light-emitting points in theemissive layer being used as design variables. A “ratio of lightextraction efficiency” between the reference device and the analyzeddevice is calculated by computing efficiency of light extraction fromthe emissive layer into the transparent member or air in both of thereference device and the analyzed device. Relation of the thickness andthe complex relative permittivity of each of the layers with the “ratioof light extraction efficiency” is found, the layers forming thereference device and the analyzed device. The respective thicknesses andthe respective complex relative permittivities of the first transparentmember, the first electrode, the first functional layer, the secondfunctional layer, the emissive layer, and the second electrode areobtained as the design variables, based on the relation and anelectroluminescence spectrum in air or the first transparent membermeasured by feeding a current to the reference device.

In another form, the second electrode is a transparent electrode, asecond transparent member is provided on a side of the second electrodeopposite to a side where the emissive layer is provided, and a complexrelative permittivity and a thickness of the second transparent memberare further included as design variables.

In another form, an optical buffer layer is further provided between thesecond electrode and the first transparent member and/or between thesecond electrode and the second transparent member, and the methodfurther includes designing a thickness, a complex relative permittivity,and a structure constant of each film forming the optical buffer film asdesign variables.

In another form, a first optical microstructure disturbing amplitude anda phase condition of light is further provided in any region between thetransparent member and the emissive layer, and the method furtherincludes designing a structure constant and a complex relativepermittivity of the first optical microstructure as design variables.

In another form, a second optical microstructure disturbing amplitudeand a phase condition of light is provided at an interface between thefirst transparent member and the outside, and a structure constant and acomplex relative permittivity of the second optical microstructure areincluded as design variables.

An electroluminescent device designed with the method of designing anelectroluminescent device based on this invention is designed with themethod of designing an electroluminescent device described in anyportion described above.

A method of manufacturing an electroluminescent device based on thisinvention includes inspecting an electroluminescent device manufacturedbased on the design variables obtained with the method of designing anelectroluminescent device described in any portion described above andmeasuring and analyzing current drive characteristics and obtaining thedesign variables with the method of designing an electroluminescentdevice described in any portion described above with the measured andanalyzed electroluminescent device being employed as the referencedevice and manufacturing an electroluminescent device based on thedesign variables.

Advantageous Effects of Invention

According to this method of manufacturing an electroluminescent device,a method of designing an electroluminescent device which allows moreaccurate computation of an external emission spectrum output to theoutside in a current injection state and accurate estimation of aquantity and/or a color of light extracted to the outside, anelectroluminescent device manufactured with the design method, and amethod of manufacturing an electroluminescent device with the designmethod can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a method of designing anelectroluminescent device in the background art.

FIG. 2 is a block diagram showing overview of a method of designing anelectroluminescent device in an embodiment.

FIG. 3 is a first cross-sectional view showing a construction example ofan electroluminescent device in an embodiment.

FIG. 4 is a second cross-sectional view showing a construction exampleof an electroluminescent device in an embodiment.

FIG. 5 is a third cross-sectional view showing a construction example ofan electroluminescent device in an embodiment.

FIG. 6 is a fourth cross-sectional view showing a construction exampleof an electroluminescent device in an embodiment.

FIG. 7 is a fifth cross-sectional view showing a construction example ofan electroluminescent device in an embodiment.

FIG. 8 is a sixth cross-sectional view showing a construction example ofan electroluminescent device in an embodiment.

FIG. 9 is a seventh cross-sectional view showing a construction exampleof an electroluminescent device in an embodiment.

FIG. 10 is an eighth cross-sectional view showing a construction exampleof an electroluminescent device in an embodiment.

FIG. 11 is a ninth cross-sectional view showing a construction exampleof an electroluminescent device in an embodiment.

FIG. 12 is a tenth cross-sectional view showing a construction exampleof an electroluminescent device in an embodiment.

FIG. 13 is an eleventh cross-sectional view showing a constructionexample of an electroluminescent device in an embodiment.

FIG. 14 is a twelfth cross-sectional view showing a construction exampleof an electroluminescent device in an embodiment.

FIG. 15 is a thirteenth cross-sectional view showing a constructionexample of an electroluminescent device in an embodiment.

FIG. 16 is a fourteenth cross-sectional view showing a constructionexample of an electroluminescent device in an embodiment.

FIG. 17 is a fifteenth cross-sectional view showing a constructionexample of an electroluminescent device in an embodiment.

FIG. 18 is a sixteenth cross-sectional view showing a constructionexample of an electroluminescent device in an embodiment.

FIG. 19 is a seventeenth cross-sectional view showing a constructionexample of an electroluminescent device in an embodiment.

FIG. 20 is an eighteenth cross-sectional view showing a constructionexample of an electroluminescent device in an embodiment.

FIG. 21 is a block diagram showing details of the method of designing anelectroluminescent device in the embodiment.

FIG. 22 is a cross-sectional view showing a construction example of anelectroluminescent device in an Example.

FIG. 23 is a diagram showing a design variable of the electroluminescentdevice employed as a reference device.

FIG. 24 is a diagram showing one example of a construction of anapparatus for measuring an external emission spectrum.

FIG. 25 is a diagram showing items of measurement data of the referencedevice.

FIG. 26 is a diagram showing selection of an item to be computed for thereference device and an analysis technique.

FIG. 27 is a diagram showing a list of items computed for an analyzeddevice in an Nth-loop.

FIG. 28 is a diagram showing a ratio of intensity and an externalemission spectrum computed for the analyzed device in the Nth-loop.

FIG. 29 is a diagram showing an example of an indicator of anelectroluminescent device which can be computed.

FIG. 30 is a diagram showing relation between a level number N in anoptimization loop and a difference Δxy from a target coordinate of acolor coordinate.

FIG. 31 is a diagram showing a design variable of an optimized device.

FIG. 32 is a diagram showing a method of manufacturing anelectroluminescent device with the method of designing anelectroluminescent device in the present embodiment.

FIG. 33 is a diagram showing a measured value and a computed value inthe Example.

FIG. 34 is a diagram showing an absolute value of an error associatedwith the measured value in the Example.

DESCRIPTION OF EMBODIMENTS

[1. Overview]

FIG. 1 shows a design method in PTDs 1 and 2 described above in a blockdiagram. Conditions assumed in computation include (1) aphotoluminescence (PL) spectrum of a light-emitting material and (2) amaterial, a refractive index, and a thickness of a light-emitting layer(S0). In step 1 (S1), a PL spectrum is set based on intensity ofgenerated light and the number of generated photons. In S2, conditionsincluding a position of a light-emitting point, a thickness, and arefractive index are set. In S3, light extraction efficiency iscomputed. In S4, desired characteristics such as intensity of externallight, the number of external photons, LPW (lumen/W), and externalquantum efficiency (EQE) are computed based on results in S1 and S3. Inorder to achieve maximization of the desired characteristics, S3 and S4are repeatedly performed (S5). Thereafter, in S6, when maximization ofthe desired characteristics is achieved, results of computationincluding a computed value, light extraction efficiency, intensity ofexternal light, the number of external photons, and desiredcharacteristics are obtained.

Thus, according to the design method described in PTDs 1 and 2, desiredexternal characteristics are computed based on light extractionefficiency computed based on the PL spectrum of the light-emittingmaterial alone and a refractive index and a thickness of thelight-emitting layer. Computation based on the photoluminescencespectrum, however, cannot achieve accurate computation of anelectroluminescence spectrum in an actual current injection state of adevice due to a microcavity effect or a difference in characteristicsbetween injection of electrons and photoexcitation. Though a spectrum inthe light-emitting layer should be assumed in the method disclosed inNPD 1, detailed description as to how an internal spectrum is to be setto lessen an error between experiments and computation is insufficient.

FIG. 2 shows overview of a method of designing an electroluminescentdevice in the present embodiment in a block diagram. Conditions assumedin computation include (1) an external emission spectrum of a referencedevice and (2) a material, a refractive index, and a thickness of alight-emitting layer (S00). In step 11 (S11), an experimental value ofthe reference device is obtained based on intensity of generated lightand the number of generated photons. In S12, a computed value of lightextraction efficiency of the reference device is obtained. In step S13,conditions including a position of a light-emitting point, a thickness,and a refractive index are set. In S14, light extraction efficiency iscomputed. In S15, a ratio of light extraction efficiency to thereference device is computed based on the values and the conditionsobtained in S12 and S14. In S16, desired characteristics such asintensity of external light, the number of external photons, LPW, andEQE are computed based on the experimental value and the ratio obtainedin S11 and S15. In order to achieve maximization of the desiredcharacteristics, S14, S15, and S16 are repeatedly performed (S17).Thereafter, in S18, when maximization of the desired characteristics isachieved, results of computation including a computed value, lightextraction efficiency, intensity of external light, the number ofexternal photons, and desired characteristics are obtained.

As described above, the present embodiment is a design method ofcomputing an external emission spectrum of an analyzed device based onan electroluminescence spectrum actually externally measured in areference device, light extraction efficiency calculated from an opticalconstant and a thickness of the reference device, and light extractionefficiency calculated from an optical constant and a thickness of theanalyzed device. By using the design technique in the presentembodiment, a method of designing an electroluminescent device allowingmore accurate computation of an external emission spectrum output to theoutside in a current injection state and accurate estimation of aquantity and/or a color of light extracted to the outside can berealized.

[2. Method of Designing Electroluminescent Device]

“2.1 Construction of Electroluminescent Device”

A construction of an electroluminescent device in the present embodimentwill be described. Though an organic electroluminescent device will bedescribed below by way of example, the present design method is notlimited to design of an organic electroluminescent device but can beemployed for design of a light-emitting diode (LED) composed of aninorganic material.

(First Electroluminescent Device)

A construction example of an “electroluminescent device having aplurality of functional layers lying between a transparent electrode anda second electrode and at least one emissive layer, a transparent memberbeing in contact with a surface of the transparent electrode opposite tothe emissive layer” as a first electroluminescent device will bedescribed below with reference to FIGS. 3 to 7. FIGS. 3 to 7 are firstto fifth cross-sectional views showing construction examples of theelectroluminescent device in the present embodiment.

In an electroluminescent device 1A shown in FIG. 3, an indium tin oxide(ITO) electrode as a transparent electrode (first electrode) 13, alight-emitting layer 14, and a metal (Ag) reflective electrode as asecond electrode 15 are formed on a first transparent member 10 in thisorder. Light-emitting layer 14 is constituted of a plurality offunctional layers and an emissive layer, and a transparent glasssubstrate is employed for first transparent member 10.

An electroluminescent device 1B shown in FIG. 4 includes a stackstructure of a conductive resin 13 a, small-thickness A1 (asmall-thickness metal electrode) 13 b, and a conductive resin 13 c astransparent electrode (first electrode) 13 as compared with theconstruction of electroluminescent device 1A.

As compared with the construction of electroluminescent device 1A, in anelectroluminescent device 1C shown in FIG. 5, light-emitting layer 14 iscomposed of an organic material, and for example, the light-emittinglayer is constituted of a hole injection layer 14 a, a hole transferlayer 14 b, an emissive layer 14 c, an electron transfer layer 14 d, andan electron injection layer 14 e. With such a construction with a largenumber of functional layers, carrier balance in emissive layer 14 c canbe improved and efficient light emission can be realized.

In an electroluminescent device 1D shown in FIG. 6, small-thickness Agis used for transparent electrode 13, and a function and effect the sameas in electroluminescent device 1C is obtained.

A metal (Ag) reflective electrode can be employed as second electrode 15in both of electroluminescent device 1C and electroluminescent device1D. Electroluminescent device 1C shown in FIGS. 5 and 6 is a bottomemission device.

Though a device having a functional layer formed on first transparentmember 10 formed from the transparent substrate (a bottom emissiondevice) is exemplified in FIGS. 3 to 6, the present embodiment isapplied also to a construction in which a reflective electrode isprovided on an opaque member (a top emission device).

FIG. 7 shows an electroluminescent device 1E representing a constructionexample of a top emission device. A reflective electrode as secondelectrode 15 is provided on a support substrate 16, and light-emittinglayer 14, small-thickness Ag as transparent electrode 13, and a sealingmember as first transparent member 10 are formed on second electrode 15in this order. Light-emitting layer 14 is constituted of electroninjection layer 14 e, electron transfer layer 14 d, emissive layer 14 c,hole transfer layer 14 b, and hole injection layer 14 a from a side ofsecond electrode 15.

In the case of the top emission device, a transparent sealing member(first transparent member 10) or inert gas for sealing or air isprovided on transparent electrode 13 in many cases. The transparentmember in the present embodiment represents the sealing member or theinert gas or air.

(Second Electroluminescent Device)

A construction example of an “electroluminescent device in which asecond electrode is a transparent electrode and a second transparentmember is provided on a side of the second electrode opposite to a sidewhere the light-emitting layer is provided” as a secondelectroluminescent device will be described below with reference toFIGS. 8 to 10. FIGS. 8 to 10 are sixth to eighth cross-sectional viewsshowing construction examples of the electroluminescent device in thepresent embodiment.

In an electroluminescent device 1F shown in FIG. 8, an ITO electrode astransparent electrode 13, light-emitting layer 14, an ITO electrode assecond electrode 15, and a second transparent member 17 are formed onfirst transparent member 10 in this order. By adopting thisconstruction, opposing surface sides are transparent and a transparentlight-emitting device emitting light from opposing surfaces or onesurface can be realized. Second transparent member 17 is formed, forexample, of an ITO or from a small-thickness metal electrode. A materialsimilar to that for first transparent member 10 is applicable to secondtransparent member 17.

In an electroluminescent device 1G shown in FIG. 9, a small-thicknessmetal film (Ag) is employed as second electrode 15 as compared with theconstruction of electroluminescent device 1F. With such a construction,a reflectance on the side of the second electrode when viewed from thelight-emitting layer is higher than a reflectance of the transparentelectrode when viewed from the light-emitting layer, and light emissionbiased to one side can be achieved.

In an electroluminescent device 1H shown in FIG. 10, as compared withthe construction of electroluminescent device 1F, a small-thicknessmetal film (Ag) is employed for both of transparent electrode 13 andsecond electrode 15. With such a construction, a reflectance of bothelectrodes when viewed from the light-emitting layer can be increased,so that luminous efficiency can be improved or color purity can beenhanced owing to a microcavity effect.

(Third Electroluminescent Device)

A construction example of an “electroluminescent device having anoptical multi-layer between the transparent electrode and thetransparent member and/or between the second electrode and the secondtransparent member” as a third electroluminescent device will bedescribed below with reference to FIGS. 11 to 13. FIGS. 11 to 13 areninth to thirteenth cross-sectional views showing construction examplesof the electroluminescent device in the present embodiment.

In an electroluminescent device 1I shown in FIG. 11, a conductive resinas transparent electrode 13, light-emitting layer 14, a small-thicknessmetal film (Ag) as second electrode 15, a dielectric multi-layer as anoptical buffer layer 18, and a large-thickness metal film (Ag) as areflection member 45 are formed on first transparent member 10 in thisorder. By adopting this construction, a color chromaticity or adistribution of light generated from the electroluminescent device canappropriately be controlled. Optical buffer layer 18 shown in FIG. 11 isapplicable also to a transparent light-emitting device.

An electroluminescent device 1J shown in FIG. 12 has a dielectricmulti-layer as a second optical buffer layer 19 between firsttransparent member 10 and transparent electrode 13 as compared with theconstruction of electroluminescent device 1I. By adopting such aconstruction, a color or a ratio of a luminance of light emitted fromopposing surfaces and a light distribution in a single-emissionlight-emitting device can optically be designed.

An electroluminescent device 1K shown in FIG. 13 has a dielectricmulti-layer as second optical buffer layer 19 between first transparentmember 10 and transparent electrode 13 and has a second transparentmember instead of a reflection member as compared with the constructionof electroluminescent device 1I. By adopting such a construction, acolor or a ratio of a luminance of light emitted from opposing surfacesand a light distribution in a dual-emission light-emitting device canoptically be designed.

(Fourth Electroluminescent Device)

A construction example of an “electroluminescent device including anoptical microstructure disturbing amplitude and a phase condition oflight between the transparent member and the emissive layer” as a fourthelectroluminescent device will be described below with reference toFIGS. 14 to 16. FIGS. 14 to 16 are twelfth to fourteenth cross-sectionalviews showing construction examples of the electroluminescent device inthe present embodiment.

In an electroluminescent device 1L shown in FIG. 14, a first opticalmicrostructure 21 including an internal scattering layer between firsttransparent member 10 and small-thickness Ag as transparent electrode 13is provided as compared with the construction of the bottom emissiondevice of electroluminescent device 1D shown in FIG. 6. First opticalmicrostructure 21 has such a structure that a smooth layer 21 c isprovided on a layer where scattering particles as a light scatteringlayer 21 b are held by a binder as a light scattering layer 21 a. Themicrostructure is such that a thickness of light scattering layer 21 bis comparable to a wavelength of light and a size of a scatteringparticle is equal to or smaller than several times as large as awavelength of light. By adopting such a construction, a waveguide modepropagating in light-emitting layer 14 can efficiently be scattered.

In an electroluminescent device 1M shown in FIG. 15, first opticalmicrostructure 21 is provided between second electrode 15 and electroninjection layer 14 e as compared with the construction ofelectroluminescent device 1E shown in FIG. 7. Microstructure 21 includesa metal projection and recess structure 21 d and a transparentconductive film 21 e.

In an electroluminescent device 1N shown in FIG. 16, the entire deviceon second electrode 12 except for first transparent member 10 is finelycorrugated as compared with the construction of electroluminescentdevice 1M shown in FIG. 15. In particular, when the opticalmicrostructure is provided on second electrode 12 serving as thereflective electrode, plasmon mode loss absorbed by the electrode canusefully be reduced. The optical microstructure described above may beprovided in electroluminescent devices 1F to 1H representing thetransparent light-emitting devices shown in FIGS. 8 to 10.

(Fifth Electroluminescent Device)

A construction example of an “electroluminescent device including asecond optical microstructure disturbing amplitude and a phase conditionof light at an interface between the transparent member and the outside”as a fifth electroluminescent device will be described below withreference to FIG. 17. FIG. 17 is a fifteenth cross-sectional viewshowing a construction example of the electroluminescent device in thepresent embodiment.

In an electroluminescent device 1O shown in FIG. 17, a second opticalmicrostructure 31 is provided on first transparent member 10 as comparedwith the construction of the bottom emission device represented byelectroluminescent device 1D shown in FIG. 6. A commercially availablelight extraction sheet can be employed as second optical microstructure31. A specific structure includes a structure in which light scatteringparticles 31 a are contained in a transparent layer 31 b and a structurein which projections and recesses are located in a surface of atransparent member as illustrated. A structure constant in this caseincludes a height and a width of projections and recesses in a surface,a period of a unit structure, or a size, a density, and a shape ofscattering particles.

Though a light-emitting layer is formed from a single layer in first tofifth electroluminescent devices 1A to 1O above, the light-emittinglayer may be formed from a plurality of layers without being limited toa single layer. FIG. 18 shows a construction example of anelectroluminescent device 1P including a plurality of emissive layers.FIG. 18 shows a cross-sectional view of electroluminescent device 1P. Inelectroluminescent device 1P, transparent electrode 13, a light-emittinglayer 14A, a charge regeneration layer 14B, a second light-emittinglayer 14C, a charge regeneration layer 14D, a third light-emitting layer14E, and reflective electrode 45 are stacked on transparent member 10 inthis order. A power supply is connected between transparent electrode 13and reflective electrode 45.

Such an electroluminescent device can generate more light with the samecurrent and is suitable for an electroluminescent device high inefficiency. The method of designing an electroluminescent device in thepresent embodiment can be applied to such an electroluminescent device.In this case, a ratio of a light-emitting dopant in each light-emittinglayer is desirably further included as a design variable. By applyingthe method of designing an electroluminescent device in the presentembodiment, a device achieving a desired spectrum and high efficiencycan efficiently be designed.

An electrode may be constructed such that a plurality of light-emittinglayers can independently be driven. FIG. 19 shows an electroluminescentdevice 1Q constructed such that a plurality of light-emitting layers canindependently be driven. FIG. 19 shows a cross-sectional view ofelectroluminescent device 1Q. In electroluminescent device 1Q,transparent electrode 13, light-emitting layer 14A, second electrode(transparent electrode) 15, second light-emitting layer 14C, a thirdelectrode (transparent electrode) 23, third light-emitting layer 14E,and reflective electrode 45 are stacked on transparent member 10 in thisorder. A power supply 1 is connected between transparent electrode 13and second electrode (transparent electrode) 15, a power supply 2 isconnected between second electrode (transparent electrode) 15 and thirdlight-emitting layer 14E, and a power supply 3 is connected betweenthird electrode (transparent electrode) 23 and reflective electrode 45.With such a construction, an electroluminescent device emitting light ofany color can be realized.

An optical buffer layer may be included between a plurality of emissivelayers as in FIG. 20. FIG. 20 shows a cross-sectional view of anelectroluminescent device 1R. In electroluminescent device 1R, anoptical buffer layer 41, transparent electrode 13, light-emitting layer14A, second electrode (transparent electrode) 15, an optical bufferlayer 42, third electrode (transparent electrode) 23, secondlight-emitting layer 14C, a fourth electrode (transparent electrode) 24,an optical buffer layer 43, a fifth electrode (transparent electrode)25, third light-emitting layer 14E, a sixth electrode (transparentelectrode) 26, an optical buffer layer 44, and reflective electrode 45are stacked on transparent member 10 in this order. Power supply 1 isconnected between transparent electrode 13 and second electrode(transparent electrode) 15, power supply 2 is connected between thirdelectrode (transparent electrode) 23 and fourth electrode (transparentelectrode) 24, and power supply 3 is connected between fifth electrode(transparent electrode) 25 and sixth electrode (transparent electrode)26.

With such a construction, a spectrum of emitted light or a lightdistribution can arbitrarily be controlled. When such an optical bufferlayer includes a microcavity adapted to a specific wavelength, a rate oflight emission at the specific wavelength can be increased. By applyingthe method of designing an electroluminescent device in the presentembodiment with an optical buffer layer also being included, aconstruction for realizing an electroluminescent device high in emissionintensity at a desired wavelength and at a desired angle can efficientlybe designed.

Though description has been given so far by way of example of asingle-emission light-emitting device, the construction including aplurality of light-emitting layers may be applicable to a dual-emissionlight-emitting device. In this case, an electroluminescent device whichemits light on opposing sides and achieves high efficiency or a desiredspectrum can efficiently be designed.

“2.2 Details of Constituent Members”

Details of various members (materials) forming electroluminescentdevices 1A to 1N described above will be described below.

(First Transparent Member 10/Second Transparent Member 17)

A material which can be used for first transparent member 10 or secondtransparent member 17 will be exemplified. For example, glass or plasticcan be exemplified, however, limitation thereto is not intended.Examples of a preferably used transparent member can include glass,quartz, and a transparent resin film.

Examples of glass include silica glass, soda lime silica glass, leadglass, borosilicate glass, and alkali free glass. From a point of viewof adhesion to a scattering layer, durability, and smoothness, a surfaceof such a glass material may be subjected to a physical treatment suchas polishing as necessary, or a coating composed of an inorganicsubstance or an organic substance or a hybrid coating which is acombination of these coatings can be formed on a surface of the glassmaterial.

Examples of the resin film include polyester such as polyethyleneterephthalate (PET) and polyethylene naphthalate (PEN), polyethylene,polypropylene, cellulose esters or derivatives thereof such ascellophane, cellulose diacetate, cellulose triacetate (TAC), celluloseacetate butyrate, cellulose acetate propionate (CAP), cellulose acetatephthalate, and cellulose nitrate, polyvinylidene chloride, polyvinylalcohol, polyethylene vinyl alcohol, syndiotactic polystyrene,polycarbonate, a norbornene resin, polymethylpentene, polyether ketone,polyimide, polyether sulfone (PES), polyphenylene sulfide, polysulfones,polyetherimide, polyether ketone imide, polyamide, a fluorine resin,nylon, polymethyl methacrylate, acrylic or polyarylates, and acycloolefin based resin such as Arton® (trademark manufactured by JSRCorporation) or Apel™ (trademark manufactured by Mitsui Chemicals,Inc.). A coating composed of an inorganic substance or an organicsubstance or a hybrid coating which is a combination of these coatingsmay be formed on the surface of the resin film.

Such a coating and a hybrid coating are each preferably a gas barrierfilm (also called a barrier film) having a water vapor permeability(25±0.5° C., relative humidity 90±2% RH) not higher than 0.01 g/(m²·24h) measured with a method in conformity with JIS K 7129-1992.Furthermore, the coating and the hybrid coating are each preferably ahigh gas barrier film having an oxygen permeability not higher than1×10⁻³ ml/(m²·24 h·atm) and a water vapor permeability not higher than1×10⁻⁵ g/(m²·24 h) which are measured with a method in conformity withJIS K 7126-1987.

A material having a function to suppress entry of a substance bringingabout deterioration of a device, such as moisture or oxygen, should onlybe adopted as a material for forming the gas barrier film as above, andfor example, silicon oxide, silicon dioxide, or silicon nitride orpolysilazane described previously can be employed. Furthermore, in orderto overcome weakness of the gas barrier film, a stack structure of suchan inorganic layer and a layer composed of an organic material (anorganic layer) is more preferably provided. Though an order of stack ofthe inorganic layer and the organic layer is not particularlyrestricted, they are preferably alternately stacked a plurality oftimes.

A method of forming a gas barrier film is not particularly limited, andfor example, vacuum vapor deposition, sputtering, reactive sputtering,molecular beam epitaxy, cluster ion beam, ion plating, plasmapolymerization, atmospheric plasma polymerization, plasma CVD, laserCVD, thermal CVD, or coating can be employed. Atmospheric plasmapolymerization described in Japanese Laid-Open Patent Publication No.2004-68143 or a method of reforming polysilazane (-containing liquid) byirradiating the same with vacuum ultraviolet rays having a wavelengthfrom 100 to 230 nm is particularly preferred.

Japanese Laid-Open Patent Publication No. 2004-68143 describes formationof a thin film with a thin film formation method using an atmosphericpressure plasma discharge treatment apparatus, by application by thesecond electrode of high-frequency electric field of which outputdensity is not lower than 1 W/cm² with relation of V1≧IV>V2 or V1>IV≧V2being satisfied, where V1 represents intensity (kV/mm) of high-frequencyelectric field applied by the first electrode, V2 represents intensity(kV/mm) of high-frequency electric field applied by the secondelectrode, and IV represents intensity (kV/mm) of electric field at thetime of start of discharging.

A thickness and a complex relative permittivity of a member are includedas design variables in the present embodiment in connection with thetransparent member. The complex relative permittivity is computed from arefractive index and an extinction coefficient using an expression (3)which will be described later, and when there is a birefringence, it isdefined as a tensor quantity having components in directions of axes inthree-dimension.

(Transparent Electrode 13/Second Electrode 15)

A material used for transparent electrode 13 or second electrode 15 willbe exemplified. For transparent electrode 13, in particular atransparent small-thickness metal having an effect to lower an effectiverefractive index of the waveguide mode and to facilitate scattering ofthe waveguide mode in the light scattering layer is desirable. Atransparent small-thickness metal layer is a small-thickness film whichis composed of a small-thickness metal and allows passage of lighttherethrough. How thin the transparent small-thickness metal layershould be in order to allow passage of light therethrough can beexpressed with an imaginary part of an refractive index. Phase variationφ and a transmittance T at the time of passage through a medium having athickness d [m] can be expressed in an expression (1) below with anrefractive index n and an extinction coefficient κ.

$\begin{matrix}{{\phi = {n\frac{2\pi}{\lambda}d}}{T = {\exp\left( {{- \kappa}\frac{4\pi}{\lambda}d} \right)}}} & (1)\end{matrix}$

In the expression, λ represents a wavelength of light in vacuum. Basedon the expression (1), a distance Ld at which intensity of light isattenuated to 1/e² can be expressed in an expression (2) below.

$\begin{matrix}{L_{d} = \frac{\lambda}{2{\pi\kappa}}} & (2)\end{matrix}$

In order to have a sufficient transmittance, the transparentsmall-thickness metal layer is desirably smaller in thickness than L_(d)shown in the expression (2).

A transparent dielectric layer is a layer composed of a dielectric.Definition of a dielectric will be described below. Whether a substanceis a metal containing many free electrons through which much light doesnot pass or a dielectric containing few free electrons through whichlight passes can be examined by using a complex relative permittivity. Acomplex relative permittivity ∈_(c) represents an optical constantassociated with interface reflection, and it represents a physicalquantity expressed with refractive index n and extinction coefficient γin an expression (3) below.∈_(c)=(n ²−κ²)+2inκP=(∈_(c)−∈_(o))E  (3)

P and E represent polarization and electric field, respectively, and∈_(o) represents a permittivity in vacuum. It can be seen from theexpression (3) that as n is smaller and κ is greater, a real part of thecomplex relative permittivity is smaller. This represents an effect ofphase shift from oscillation of electric field, of polarization responsedue to oscillation of electrons.

The negative real part of the complex relative permittivity expressed inthe expression (3) means that electric field oscillation andpolarization response are reversed, which represents characteristics ofthe metal. In contrast, when the real part of the complex relativepermittivity is positive, a direction of electric field and a directionof polarization response match with each other and polarization responseas a dielectric is exhibited. In summary, a medium of which real part ofa complex relative permittivity is negative is a metal, and a substanceof which real part of the complex relative permittivity is positive is adielectric.

In general, a lower refractive index n and a greater extinctioncoefficient κ mean a material of which electrons well oscillate. Amaterial high in electron transferability tends to be low in refractiveindex n and great in extinction coefficient κ.

In particular, a metal electrode has n around 0.1 whereas it has a largevalue for extinction coefficient κ from 2 to 10, and it is also high inrate of change with a wavelength. Therefore, even when a value forrefractive index n is the same, a value for extinction coefficient κ issignificantly different, and there is a great difference in performancein transfer of electrons in many cases.

In carrying out the present embodiment, a metal low in refractive indexn for lowering in effective refractive index of the waveguide mode andhigh in extinction coefficient κ for improvement in response ofelectrons is desirable. For example, aluminum (Al), silver (Ag), andcalcium (Ca) are desirable. In other examples, gold (Au) which is alsoadvantageously less prone to oxidization is possible. Another materialis exemplified by copper (Cu), and this material is high inconductivity. Other materials which have good thermal properties orchemical properties, are less prone to oxidization even at a hightemperature, and do not chemically react with a material for a substrateinclude platinum, rhodium, palladium, ruthenium, iridium, and osminium.An alloy containing a plurality of metal materials may be employed. Inparticular, MgAg or LiAl is often used for a small-thickness transparentmetal electrode.

For a transparent electrode in a transparent electrode layer, inaddition to a transparent oxide semiconductor, a conductive resin whichcan be produced at low cost with an application method may be employed.A perylene derivative or a fullerene derivative such as[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is available as aconductive resin material used for an electron transfer electrode. Forexample, in a case of PCBM, an optical constant of visible light isrefractive index n=2.2 and extinction coefficient κ=0.25 and areflectance of an electrode viewed from the light-emitting layer ishigher than that of a resin having refractive index n=1.5.

Examples of a conductive resin material used for a hole transferelectrode include poly(3,4-ethylenedioxythiophene)(PEDOT)/poly(4-styrenesulfonate) (PSS), poly(3-hexylthiophene) (P3HT),poly(3-octylthiophene) (P3OT), poly(3-dodecylthiophene-2,5-diyl)(P3DDT), and a copolymer of fluorene and bithiophene (F8T2). Forexample, in a case of PEDOT/PSS, an optical constant of visible light isrefractive index n=1.5 and extinction coefficient κ=0.01, and areflectance of an electrode viewed from the light-emitting layer has avalue comparable to that of a resin having an refractive index n=1.5 andthe reflectance is relatively lower than that of PCBM.

In order to enhance electrical conductivity of the transparent electrodelayer, a metal mesh, a metal nanowire, or metal nanoparticles may beused together. In this case, with higher electron conductivity of anelectrode including a metal nanowire, an average refractive index tendsto be lower and a reflectance viewed from the light-emitting layer tendsto be high. In carrying out the present embodiment, light of whichwaveguide mode has been scattered by a material for the transparentelectrode low in reflectance viewed from the light-emitting layer canefficiently be extracted into the transparent substrate, which isdesirable. When a metal mesh, a metal nanowire, or metal nanoparticlesis (are) used, an effect of extraction to the outside by scattering ofthe waveguide mode by the electrode itself is also achieved, which isdesirable in realizing a light-emitting device high in efficiency.

A thickness and a complex relative permittivity of a member are includedas design variables in the present embodiment in connection with thetransparent electrode. The complex relative permittivity is computedfrom a refractive index and an extinction coefficient using theexpression (3), and when there is a birefringence, it is defined as atensor quantity having components in directions of axes inthree-dimension. When the transparent electrode is formed from aplurality of members, a variable for determining a structure of eachmember and a complex relative permittivity are included as designvariables. For example, in the case of a metal mesh electrode, a heightor a width of the mesh, a period, a material, and a combination ofmaterials may be included as design variables.

(Emissive Layer 14 c/Functional Layer)

When an organic material is used for emissive layer 14 c or thefunctional layer, the material typically has a refractive index between1.6 and 1.8 in a visible light range. From a point of view of preferablyobtaining improvement in external extraction quantum efficiency of adevice or longer life of light emission, an organic metal complex as amaterial for an organic EL device is preferably used as a material forthe emissive layer. Furthermore, a metal involved with formation of acomplex is preferably any one metal belonging to group VIII to group Xin the periodic table, Al, or Zn, and particularly preferably, the metalis Ir, Pt, Al, or Zn.

A thickness and a complex relative permittivity of a member are includedas design variables in the present embodiment in connection with theemissive layer. The complex relative permittivity is computed from arefractive index and an extinction coefficient using the expression (3),and when there is a birefringence, it is defined as a tensor quantityhaving components in directions of axes in three-dimension. When theemissive layer is formed from a plurality of members, a variable fordetermining a structure of each member and a complex relativepermittivity are included as design variables.

(Reflective Electrode (Second Electrode) 15)

A metal material exemplified as a material for the transparentsmall-thickness metal layer can be employed as a material for thereflective electrode. Other alloys and an ink containing metalnanoparticles may be employed. In addition, a transparent electrode anda dielectric multi-layer mirror, a metal projection and recessstructure, or a photonic crystal may be used in combination with areflection layer. When the dielectric multi-layer mirror, the metalprojection and recess structure, or the photonic crystal is used for areflection layer, plasmon loss in the reflection layer is advantageouslyeliminated.

A thickness and a complex relative permittivity of a member are includedas design variables in the present embodiment in connection with thereflective electrode. The complex relative permittivity is computed froma refractive index and an extinction coefficient using the expression(3), and when there is a birefringence, it is defined as a tensorquantity having components in directions of axes in three-dimension.When the reflective electrode is formed from a plurality of members, avariable for determining a structure of each member and a complexrelative permittivity are included as design variables.

(Optical Buffer Layer)

A photonic crystal structure in addition to the dielectric multi-layercan be employed for the optical buffer layer. In order to fabricate thedielectric multi-layer or the photonic crystal structure, materialshaving a plurality of permittivities should be combined, and thedielectric materials are desirably transparent at a wavelength at whichlight is generated in the emissive layer. A material used for thetransparent member can be made use of as a transparent material.Specific materials can include TiO₂ (having refractive index n=2.5) andSiO_(x) (having refractive index n=1.4 to 3.5). Other examples of thedielectric materials can include diamond, calcium fluoride (CaF), andsilicon nitride (Si₃N₄).

Examples of a resin material include vinyl chloride, acrylic,polyethylene, polypropylene, polystyrene, ABS, nylon, polycarbonate,polyethylene terephthalate, polyvinylidene fluoride, Teflon™, polyimide,and a phenol resin, and there are also resin materials having arefractive index from 1.4 to 1.8. There is also a technique to control arefractive index to be higher or lower by mixing nanoparticles, and arefractive index of a plastic material in which hollow nano silica ismixed can be closer to 1. A refractive index close to 2 can also berealized by mixing particles of a material high in refractive index suchas TiO₂ into a resin.

A thickness and a complex relative permittivity of a member forming abuffer layer are included as design variables in the present embodimentin connection with the optical buffer layer. The complex relativepermittivity is computed from a refractive index and an extinctioncoefficient using the expression (3), and when there is a birefringence,it is defined as a tensor quantity having components in directions ofaxes in three-dimension. When the optical buffer layer is formed from aplurality of members, a variable for determining a structure of eachmember and an optical constant are included as design variables. Forexample, when the optical buffer layer is formed from a dielectricmulti-layer, a thickness and a complex relative permittivity of eachoptical thin film forming the dielectric multi-layer may be included asdesign variables. When the optical buffer layer is formed, for example,of photonic crystals, a dielectric structure of a unit lattice ofphotonic crystals and a complex relative permittivity of a materialforming the unit lattice may be included as design variables.

(Optical Microstructure)

Examples of the optical microstructure include a layer containingscattering particles, a layer having a projection and recess structure,and such a structure that a light-emitting layer as a whole has acorrugated structure. In any case, design variables include a variablefor determining a size or a shape of the structure and a complexrelative permittivity of each structure. The complex relativepermittivity is computed from a refractive index and an extinctioncoefficient using the expression (3), and when there is a birefringence,it is defined as a tensor quantity having components in directions ofaxes in three-dimension.

“2.3 Method of Computing Light Extraction Efficiency and VariousCharacteristics of External Light”

A method of computing light extraction efficiency in the presentembodiment will be described in the present section. Light extractionefficiency refers to the number of photons extracted into a transparentmember or air when the number of photons generated in an emissive layeris defined as 1. Though a computation method disclosed on PTDs 1 and 2shown in the background art (hereinafter referred to as the computationmethod in the background art) can be employed for a specific computationmethod, the computation method in the background art and the computationmethod in the present embodiment are different from each other in twopoints below.

A first difference between the computation method in the background artand the computation method in the present embodiment is “calculating ‘aratio of light extraction efficiency’ between a reference device and ananalyzed device by computing efficiency in light extraction from anemissive layer into a transparent member or air in both of the referencedevice and a desired analyzed device and finding relation of a thicknessand a complex relative permittivity of each of the layers forming thereference device and the analyzed device with the ‘ratio of lightextraction efficiency.’” Thus, a difference between a photoluminescencespectrum and an electroluminescence spectrum caused by injection ofelectrons or the microcavity effect in experiments can be corrected bythe experiments.

A second difference between the computation method in the background artand the computation method in the present embodiment is performing“quantum optical analysis.” Characteristics to which attention is paidin the present embodiment are various characteristics of external lightat the time of injection of electrons. Though the computation method inthe background art does not provide description, internal quantumefficiency should be found based on quantum optical analysis in order tocompute characteristics at the time of injection of electrons. Ingeneral, change in light emission rate owing to the microcavity effectis computed, and precise computation is carried out by solving a rateequation involved with radiative recombination. For the sake of brevity,an example in which only radiative recombination and non-radiativerecombination are present will be described here. A rate equationinvolved with radiative recombination is written as in an expression (4)below, where k_(r) represents a radiative recombination rate and k_(nr)represents a non-radiative recombination rate.

$\begin{matrix}{\frac{{dN}_{exc}}{dt} = {{{- \left( {k_{r} + k_{nr}} \right)}N_{exc}} + N_{inj}}} & (4)\end{matrix}$

In the expression, N_(exc) represents a density of exciters in theemissive layer and N_(inj) represents a density of injection ofexciters. Since temporal differentiation is zero in a steady state,ultimately, an expression (5) below holds.

$\begin{matrix}{{N_{inj} = {\left. {\left( {k_{r} + k_{nr}} \right)N_{exc}}\Rightarrow N_{exc} \right. = \frac{N_{inj}}{k_{r} + k_{nr}}}}{\Gamma_{rad} = {{k_{r}N_{exc}\mspace{31mu}\Gamma_{nr}} = {k_{nr}N_{exc}}}}} & (5)\end{matrix}$

A probability φ of radiative recombination is computed as in anexpression (6) below.

$\begin{matrix}{\phi = {\frac{\Gamma_{rad}}{\Gamma_{rad} - \Gamma_{nr}} = \frac{k_{r}}{k_{r} + k_{nr}}}} & (6)\end{matrix}$

A radiative recombination rate can be computed by combining emissionlifetime specific to a material with the computation method disclosed inNPD 1. In addition, a radiative recombination rate can be analyzed bycombining emission lifetime specific to a material with afinite-difference time-domain (FDTD) method or a transfer matrix methodrepresenting existing electromagnetic field analysis techniques. Inparticular, in computation of a radiative recombination rate, a Purcellfactor disclosed in NPD 1 is desirably included in a result ofcomputation.

A guideline for more accurate computation is shown below. Since kr isdependent on a structure of a device and an emission wavelength,weighting computation is desirably carried out also in consideration ofdependency on a structure of a device and dependency on a wavelength. Inthe case of an organic electroluminescent device, more accurate analysisis performed by incorporating an effect of excited triplet deactivationor singlet-triplet deactivation into the rate equation, and a correctionfactor for “light extraction efficiency” is computed.

Finally, the number of photons extracted to the outside (externalquantum efficiency: EQE) standardized by the number of injectedelectrons is computed as in an expression (7).EQE=γ_(e)×φ×η_(OE)  (7)

In the expression, γ_(e) represents efficiency in conversion from anelectron into an exciter determined under spin injection rules, φrepresents a probability of radiative recombination, and η_(OE)represents “efficiency of light extraction” into a transparent member orair and it is a value including quantum optical analysis.

The overall specific computation method will be shown below. Dependencyη₀ (λ) on a wavelength of light extraction efficiency of the referencedevice and light extraction efficiency η₁ (λ) of the analyzed device arecomputed by combining the computation method in the background art (theexisting analysis technique) and quantum optical computation. S₀ (λ)represents a whole-angle optical spectrum in air of the reference devicemeasured in experiments. A whole-angle spectrum S₁ (λ) in air of theanalyzed device is computed in an expression (8) below.

$\begin{matrix}{{S_{1}(\lambda)} = {\frac{\eta_{1}(\lambda)}{\eta_{o}(\lambda)}{S_{o}(\lambda)}}} & (8)\end{matrix}$

Thereafter, a front spectrum S_(front) (λ) of the analyzed device iscalculated as in an expression (9) below, based on a ratio G_(front) (λ)between the whole-angle spectrum in air found in computation and a frontspectrum in air.

$\begin{matrix}{{S_{front}(\lambda)} = {{{G_{front}(\lambda)}{S_{1}(\lambda)}} = {{G_{front}(\lambda)}\frac{\eta_{1}(\lambda)}{\eta_{o}(\lambda)}{S_{o}(\lambda)}}}} & (9)\end{matrix}$

This is also applicable to spectra at other angles. An expression (10)below holds where G_(ang)(λ, θ) represents a ratio between thewhole-angle spectrum in air found in computation and an angle spectrum.

$\begin{matrix}{{S_{ang}\left( {\lambda,\theta} \right)} = {{{G_{ang}\left( {\lambda,\theta} \right)}{S_{1}(\lambda)}} = {{G_{ang}\left( {\lambda,\theta} \right)}\frac{\eta_{1}(\lambda)}{\eta_{o}(\lambda)}{S_{o}(\lambda)}}}} & (10)\end{matrix}$

A color coordinate or a luminous flux [lm] after a desired spectrum isfound can be computed under the definition by CIE.

This computation method is applicable not only to the whole-anglespectrum in air but also to a whole-angle spectrum in the inside of atransparent member. Specifically, a method of conducting measurementwith the use of an integrating sphere by bringing a hemispherical lenssufficiently larger than a light emitting region into intimate contactwith a transparent member with the use of a matching oil is available asa method of finding a whole-angle spectrum in the inside of thetransparent member in experiments.

“2.4 Technique of Optimization Computation”

A desirable method of optimization computation will be described withreference to FIG. 2. External quantum efficiency, an emission luminance,and a color coordinate are computed by computing an external spectrumwith the method described in “2.3 Method of Computing Light ExtractionEfficiency and Various Characteristics of External Light” for eachdesign variable of the electroluminescent device.

Briefly speaking, a method of achieving a desired color coordinate orefficiency by performing exhaustive computation in a desired range ofdesign variables is possible. In this case, many levels are efficientlycomputed with fewer levels based on computation under adesign-of-experiments method. Efficiency in computation is high if eachlevel is subjected to parallel computation by a plurality of clustermachines. Parallel computation using a graphic processor is desirablefor acceleration of computation.

Combination with optimization computation is desirable. An optimizationalgorithm is desirably combined with a steepest descent method, aconjugate gradient method, a linear programming method, or a geneticalgorithm relating to desired characteristics. In optimization,optimization in consideration of robustness is desirably performed. Atechnique to perform computation a plurality of times for designvariables around a certain level, evaluate a level based on magnitude ofvariation in desired characteristics, and select a level less invariation is desirable as a specific method of computing robustness.

[3. Details of Design Method]

“3.1 Overview”

FIG. 21 shows a procedure of the design method in the presentembodiment. This design technique is constituted of a section R100 inwhich current drive characteristics and analysis of the reference deviceare mainly performed and an optimization loop 200 for the analyzeddevice. A design method of an essential part of the design method in thepresent embodiment will be described below.

Section R100 where current drive characteristics and analysis areperformed determines design variables of a reference device based on athickness, a complex relative permittivity, and a structure constant(S110). Thereafter, a reference device is fabricated (S120). Then,measurement of the reference device is conducted (S130). Specifically,an electroluminescence spectrum in current drive is measured, andexternal quantum efficiency in current drive is measured. A result ofmeasurement of the reference device is input to S250 in optimizationloop R200 which will be described later.

Computation of the reference device is performed (S140) based ondetermination of the design variables of the reference device (S110).Specifically, computation of the reference device is performed by usingquantum optical analysis, electromagnetic field analysis, and ray trace.A result of computation of the reference device is input to S240 inoptimization loop R200 which will be described later.

In optimization loop R200, design variables of the analyzed device aredetermined based on a thickness, a complex relative permittivity, and astructure constant (S210). Thereafter, computation of the analyzeddevice is performed (S220). Specifically, computation of the analyzeddevice is performed by using quantum optical analysis, electromagneticfield analysis, and ray trace.

Then, results of computation of the analyzed device are obtained (S230).Specifically, results of computation of dependency on a wavelength of arelative light emission rate, dependency on a wavelength of lightextraction efficiency, and dependency on a wavelength and an angle ofintensity of light emission of the device are obtained.

Then, a ratio of emission intensity between the analyzed device and thereference device is computed based on the results of computation in S140and the results of computation in S230. Specifically, a ratio inconnection with dependency on a wavelength of a relative light emissionrate, dependency on a wavelength of light extraction efficiency, anddependency on a wavelength and an angle of intensity of light emissionof the device is computed.

Then, an electroluminescence spectrum of the analyzed device is computedbased on the results of computation in S240 and S130 (S250).Specifically, dependency on a wavelength of light extraction efficiencyand dependency on a wavelength and an angle of intensity of lightemission of the device are computed.

Then, desired characteristics of the analyzed device are computed (S260)based on the results of computation obtained in S250. Specifically,external quantum efficiency, a front luminance, a front colorcoordinate, dependency on an angle of the color coordinate, luminousefficiency [lm/w], and an emission spectrum and dependency on an anglethereof, and a characteristic value calculated from electric powerefficiency are computed.

Then, the design variables are varied so as to be closer to targetvalues (S270) based on comparison between the target values of thedesired characteristics and analyzed values based on the results ofcomputation of the desired characteristics of the analyzed device inS260. In this case, random computation, the design-of-experimentsmethod, the steepest descent method, the Newton method, the conjugategradient method, or a genetic algorithm is employed as the computationmethod. Thereafter, the process returns to S210, where the designvariables of the analyzed device are determined (S210) and optimizationloop R200 is executed.

The present embodiment relates to the method of designing anelectroluminescent device having a plurality of functional layers lyingbetween the transparent electrode and the second electrode and at leastone emissive layer, the transparent member being in contact with thesurface of the transparent electrode opposite to the emissive layer. Anorganic EL electroluminescent device 100 as shown in FIG. 22 representsa typical example of the electroluminescent device.

In organic EL electroluminescent device 100 shown in FIG. 22, ITO(having a thickness of 150 nm) as a transparent electrode 113 isprovided on a glass substrate as a transparent member 110, and a firstfunctional layer 114 a, an emissive layer 114 c (having a thickness of20 nm), and a second functional layer 114 e are provided through vapordeposition. Thereafter, an Ag film (having a thickness of 100 nm) whichis a reflective electrode is provided as second electrode 15. A greenphosphorescent material having an emission peak wavelength of 520 nm isemployed for emissive layer 114 c. A hole injection layer, a holetransfer layer, and an electron blocking layer (a total of 35 nm) areprovided in first functional layer 114 a. A hole blocking layer, anelectron transfer layer, and an electron injection layer (a total of xnm) are provided in second functional layer 114 e. Transparent member110 is in contact with a surface of transparent electrode 113 oppositeto emissive layer 114 c.

Design variables in design of organic EL electroluminescent device 100shown in FIG. 22 include a thickness and a complex relative permittivityof each of transparent member 110, transparent electrode 113, firstfunctional layer 114 a, second functional layer 114 e, and secondelectrode 115 as well as positions and a distribution of light-emittingpoints in emissive layer 114 c.

The design method in the present embodiment aims to realize a designoptimizing external characteristics in current drive. The externalcharacteristics in current drive represent indicators as desiredcharacteristics shown in FIG. 29 which will be described later and anyindicator computed by using values in FIGS. 23 and 25 to 28 which willbe described later. Examples of specific indicators include electricpower efficiency, current efficiency, external quantum efficiency, afront luminance, a front color coordinate (x, y), a front colortemperature, a color rendering property, and dependency on an angle ofthe color coordinate. A method of analysis in each step in FIG. 21 willbe described below.

“3.2 Measurement and Analysis of Current Drive Characteristics ofReference Device”

(3.2.1 Determination of Design Variables of Reference Device andFabrication of Reference Device)

Design variables of a reference device are initially determined (S110).Typically, fabrication with a thickness minimum required forimplementing each function is desirable. An example in which a thicknessshown in FIG. 22 and x=50 nm are set will be described. The referencedevice can be fabricated with vacuum deposition. FIG. 23 summarizesdesign variables used for the reference device. The design variablesinclude a thickness and a complex relative permittivity of eachconstituent member.

Transparent substrate 110 is formed from a glass substrate and has athickness of 700 micrometers (0.7 mm) and a complex relativepermittivity of ∈1. Transparent electrode 113 is composed of ITO and hasa thickness of 150 nm and a complex relative permittivity of ∈2. Firstfunctional layer 114 a is constituted of a hole injection layer, a holetransfer layer, and an electron blocking layer and has a thickness of 35nm and a complex relative permittivity of ∈3. Emissive layer 114 c isformed from a light-emitting layer and has a thickness of 20 nm and acomplex relative permittivity of ∈4. Second functional layer 114 e isconstituted of a hole blocking layer, an electron transfer layer, and anelectron injection layer and has a thickness of 50 nm and a complexrelative permittivity of ∈5. Second electrode 115 is formed from an Agfilm and has a thickness of 100 nm and a complex relative permittivityof ∈6. A position of a light-emitting point is located at the center ofemissive layer 114 c and a distribution is such that the light-emittingpoints are concentrated to the center like a delta function.

(3.2.2 Measurement of Reference Device)

An external emission spectrum is measured (S130) by applying a voltageto an electrode of the fabricated reference device (S120). FIG. 24 showsone example of a construction of an apparatus 1000 for measuring anexternal emission spectrum. A whole-angle spectrum is desirably measuredby using an integrating sphere 1100 as the external emission spectrum ofreference device 100. Therefore, reference device 100 is placed at acentral portion of integrating sphere 1100 with the use of a base 1200.

In measuring a spectrum of reference device 100, a spectrometer 1400 isdesirably used to record the number of photons for each wavelength in acontrol device 1300. A condition (a current and a voltage) of a powersupply supplied to reference device 100 is recorded in control device1300 in measurement. By doing so, measurement data of reference device100 can be used for subsequent analysis.

FIG. 25 shows specific examples of measurement data. Measurement dataincludes a drive current (a notation I_(in) and a unit [A]), a drivevoltage (a notation V_(in) and a unit [V]), an electroluminescencespectrum (a notation S_(EL1) (λ) and a unit [/s/nm]), an area of adevice (a notation S_(dev) and a unit [m²]), a temperature of a device(a notation T_(dev) and a unit [K]), a front luminance (a notationI_(cd) and a unit [cd/m²]), a front color chromaticity x (a notation xand a unit dimensionless), a front color chromaticity y (a notation yand a unit dimensionless), and a front color temperature (a notation Tand a unit [K]).

Data (for example, a barometric pressure) not shown in FIG. 25 isdesirably recorded when it is necessary for subsequent analysis.Measurement of the external emission spectrum in a unit of the number ofphotons per unit time and unit wavelength facilitates conversion ofcharacteristics such as external quantum efficiency. Theelectroluminescence spectrum measured here has been converted to thenumber of photons per unit time and unit wavelength. Anelectroluminescence spectrum measured in another unit can also beconverted to the number of photons per unit time and unit wavelengthbased on a measurement condition. Conversion to an intensity spectrumcan be carried out by multiplying a light spectrum in a unit of thenumber of photons by energy per one photon.

(3.2.3 Computation of Reference Device)

Referring back to FIG. 21, computation of the reference device iscontinued (S140). Computation of the reference device includes such atechnique as quantum optical analysis, electromagnetic field analysis,and ray trace, and items which can be computed are different thereamong.FIG. 26 summarizes selection of items to be computed and an analysistechnique.

Examples of items to be computed include dependency on a wavelength of arelative radiative recombination rate (Purcell factor) (a notation F₁(λ), a unit dimensionless, and an analysis technique (quantum opticalanalysis·electromagnetic field analysis)), efficiency of lightextraction into air (a notation η_(Air1) (λ), a unit dimensionless, andan analysis technique (electromagnetic field analysis·ray trace)), adistribution of angles of light intensity in air at a specificwavelength (a notation D_(Air1) (λ), a unit [/sr], and an analysistechnique (electromagnetic field analysis·ray trace)), efficiency oflight extraction into the transparent member (a notation η_(Sub1) (λ), aunit dimensionless, and an analysis technique (electromagnetic fieldanalysis·ray trace)), and a distribution of angles of light intensity inthe transparent member at a specific wavelength (a notation D_(Sub1)(λ), a unit [/sr], and an analysis technique (electromagnetic fieldanalysis·ray trace)).

In any analysis, the design variables shown in FIG. 23 are used foranalysis. Regarding each analysis technique, computation can beperformed based on PTDs 1 and 2 and the electromagnetic field analysistechnique. The distribution of angles of intensity is standardized suchthat 1 is attained when integrated by multiplying a solid angle (see anexpression 11). In design of a device emitting light from opposingsurfaces, standardization in the expression 11 is performed for lightemission in each direction.

$\begin{matrix}{{\int_{0}^{\pi/2}{{D_{{Air}\; 1}\left( {\lambda,\theta} \right)}2\pi\;\sin\;\theta\; d\;\theta}} = {{1\mspace{31mu}{\int_{0}^{\pi/2}{{D_{{Sub}\; 1}\left( {\lambda,\theta} \right)}2\pi\;\sin\;\theta\; d\;\theta}}} = 1}} & (11)\end{matrix}$

Purcell factor represents a ratio of a radiative recombination rate whenthere is a microcavity formed of a dielectric or a metal in thesurroundings to a radiative recombination rate of a light-emittingmaterial alone, and it corresponds to F (λ) in NPD 1. Description ofmeasurement and analysis of current drive characteristics of thereference device thus ends.

“3.2 Optimization Loop”

Each procedure in the optimization loop will be described below withreference to FIG. 21.

(3.3.1 Determination of Design Variables of Analyzed Device)

Design variables of a device to be analyzed are determined (S210). Avalue of the design variable shown in FIG. 23 is varied. A specificmethod of varying a value includes the steepest descent method and agenetic algorithm as enhancing desired characteristics which will bedescribed later. A combination of input variables is converted to avector, and a first loop is expressed as x[1], a second loop isexpressed as x[2], . . . , and an Nth loop is expressed as x[N].

(3.3.2 Computation of Analyzed Device)

Then, computation of the analyzed device is performed (S220 and S230).An item computed here is the same as the item to be computed of thereference device shown in FIG. 26. Attention should be paid to the factthat, with regard to design variables, change to the first loopexpressed as x[1], the second loop expressed as x[2], . . . , and theNth loop expressed as x[N] is made. A notation as defined in FIG. 27 isdetermined for the result of analysis of the Nth loop.

Items to be computed of the analyzed device in the Nth loop includedependency on a wavelength of a relative radiative recombination rate(Purcell factor) (a notation F [N] (λ), a unit dimensionless, and ananalysis technique (quantum optical analysis·electromagnetic fieldanalysis)), efficiency of light extraction into air (a notation η_(Air)[N] (λ), a unit dimensionless, and an analysis technique(electromagnetic field analysis·ray trace)), a distribution of angles oflight intensity in air at a specific wavelength (a notation D_(Air) [N](λ), a unit [/sr], and an analysis technique (electromagnetic fieldanalysis·ray trace)), efficiency of light extraction into a transparentmember (a notation η_(Sub) [N] (λ), a unit dimensionless, and ananalysis technique (electromagnetic field analysis·ray trace)), and adistribution of angles of light intensity in the transparent member at aspecific wavelength (a notation D_(Sub) [N](λ), a unit [/sr], and ananalysis technique (electromagnetic field analysis·ray trace)). Lightextraction efficiency represents a ratio of light generated in theemissive layer which exits into air or a transparent member. Computationof light extraction efficiency of external quantum efficiency (EQE) isdesirably corrected with the method in NPD 1 by using dependency on awavelength of a relative radiative recombination rate (Purcell factor)described previously. By doing so, light extraction efficiency incurrent injection can accurately be computed.

(3.3.3 Computation of Ratio of Emission Intensity Between AnalyzedDevice and Reference Device and Electroluminescence Spectrum)

A ratio for computing an electroluminescence spectrum of the analyzeddevice is computed by using measurement items measured in currentinjection of the reference device shown in FIG. 25 (S240). Anelectroluminescence spectrum of the analyzed device is computed by usingthe intensity ratio described above (S250). Items computed here andnotations are defined as in FIGS. 28 and 29.

Referring to FIG. 28, items to be computed of the analyzed device in theNth loop include a ratio of intensity of energy which comes out into airto the reference device (a notation G_(Air) [N] (λ) and a unitdimensionless), a ratio of intensity of energy which comes out into thetransparent member to the reference device (a notation G_(Sub) [N] (λ)and a unit dimensionless), a computed value of an electroluminescencespectrum (a notation S_(EL) [N] (λ) and a unit [/s/nm]), and a computedvalue of an electroluminescence spectrum in the transparent member (anotation S_(EL) _(_) _(Sub) [N] (λ) and a unit [/s/nm]).

Referring to FIG. 29, an indicator value computed for the analyzeddevice in the Nth loop include electric power efficiency (a notation LPW[N] and a dimension [lm/W]), current efficiency (a notation LPA [N] anda dimension [lm/A]), external quantum efficiency (a notation EQE [N] anddimensionless), a front luminance (a notation Y [N] and a dimension[cd/m²]), a front color coordinate x (a notation x [N] anddimensionless), a front color coordinate y (a notation y [N] anddimensionless), a front color temperature (a notation T [N] and [K]), afront color rendering property (a notation Ra [N] and dimensionless),dependency x on an angle of the color coordinate (a notation x_(θ) [N](θ) and dimensionless), and dependency y on an angle of the colorcoordinate (a notation y_(θ) [N] (θ) and dimensionless).

Measurement of reference device 100 shown in FIG. 24 is described asmeasurement of a spectrum which comes out into outside air of thedevice. A ratio of intensity and a computed value of the externalemission spectrum shown in FIG. 28 are computed in an expression (12)using an experimental electroluminescence spectrum shown in FIG. 25.

$\begin{matrix}\left. \begin{matrix}{{{G_{Air}\lbrack N\rbrack}(\lambda)} = \frac{{S_{EL}\lbrack N\rbrack}(\lambda)}{S_{{EL}\; 1}(\lambda)}} \\{{{S_{EL}\lbrack N\rbrack}(\lambda)} = {{G_{Air}\lbrack N\rbrack}(\lambda){S_{{EL}\; 1}(\lambda)}}} \\{{{G_{Sub}\lbrack N\rbrack}(\lambda)} = \frac{{S_{EL\_ Sub}\lbrack N\rbrack}(\lambda)}{S_{{EL}\; 1}(\lambda)}} \\{{{S_{EL\_ Sub}\lbrack N\rbrack}(\lambda)} = {{G_{Sub}\lbrack N\rbrack}(\lambda){S_{{EL}\; 1}(\lambda)}}}\end{matrix} \right\} & (12)\end{matrix}$

A ratio of intensity of energy which comes out into air between thereference device and the analyzed device is computed with the existingquantum optical analysis technique, the electromagnetic field analysistechnique, and the ray trace technique shown in FIG. 27.

What is important here is computation of an electroluminescence spectrumof the analyzed device (S240 and S250) by using a measured value of theelectroluminescence spectrum of the reference device (S130), the resultof computation of the reference device (S140), and the result ofcomputation of the analyzed device (S230). By carrying out computationas such, an external light emission electroluminescence spectrum incurrent injection can accurately be computed.

(3.3.4 Computation of Desired Characteristics of Analyzed Device)

A distribution of wavelengths of external emission spectra and adistribution of angles of light intensity in air or in the inside of thetransparent member in any Nth computation are analyzed (S260) based onthe results of analysis until the section 3.3.3. When one is interestedin a color coordinate of emitted light, a color coordinate can becomputed by carrying out computation under the definition by CommissionInternationale de l'Eclairage (CIE) by using the computed spectrum andthe distribution of angles.

Electric power efficiency of the analyzed device can also be computedbased on the conditions for driving the reference device shown in FIG.25 and the results of computation shown in FIGS. 26 to 28. A luminanceor a distribution of angles of the color coordinate can also be computedby using characteristics of the distribution of angles shown in FIG. 27.FIG. 29 lists indicators which can be computed as desiredcharacteristics.

Desired characteristics are not limited to the indicators listed in FIG.29 but also may include any indicator which is computed by using valueslisted in FIGS. 23 and 25 to 28. For example, when variation inindicator value resulting from minor variation in certain designvariable in the vicinity of the certain design variable is employed as anew indicator value and optimization is carried out so as to minimizethe variation, a robust design solution can be derived and design can besuited to mass production. Though not shown in FIG. 29, a colorrendering property of color samples from R1 to R15 may independently beevaluated other than Ra as an indicator for the color renderingproperty. By thus independently evaluating a color rendering property ofcolor samples, which color is well reproduced can be quantified andperformance as lighting can more finely be designed.

(3.3.5 Comparison of Target Value with Analyzed Value of DesiredCharacteristics and Change Design Variable to be Closer to Target Value)

As Nth design variable x [N] which is a set of design variables as avector is determined based on the description so far, desiredcharacteristics exemplified in FIG. 30 are computed from theelectroluminescence spectrum of the reference device found inexperiments.

Referring to FIG. 30, regarding the design variables of an optimizeddevice, transparent substrate 110 is formed from a glass substratehaving a thickness of 700 micrometers (0.7 mm) and a complex relativepermittivity of ∈1. Transparent electrode 113 is composed of ITO and hasa thickness of 150 nm and a complex relative permittivity of ∈2. Firstfunctional layer 114 a is constituted of a hole injection layer, a holetransfer layer, and an electron blocking layer and has a thickness of 37nm and a complex relative permittivity of ∈3. Emissive layer 114 c isformed from a light-emitting layer and has a thickness of 20 nm and acomplex relative permittivity of ∈4. Second functional layer 114 e isconstituted of a hole blocking layer, an electron transfer layer, and anelectron injection layer and has a thickness of 113 nm and a complexrelative permittivity of ∈5. Second electrode 115 is formed from an Agfilm and has a thickness of 100 nm and a complex relative permittivityof ∈6.

N+1th computation is carried out based on this result, and desiredcharacteristics are brought closer to target values (S270). An algorithmfor repeated computation includes the steepest descent method, theconjugate gradient method, and a genetic algorithm as enhancing desiredcharacteristics. Any existing optimization algorithm may be employed.Referring back to the Section 3.3.1, optimization loop R200 iscontinued. Optimization loop R200 ends when it is determined thatdesired characteristics are sufficiently close or the defined number ofrepetitions is completed.

In optimization, an evaluation function is desirably determined and analgorithm is designed so as to minimize or maximize the evaluationfunction. For example, in optimization to bring the front colorcoordinate (x, y) closer to a target color coordinate (x_(target),y_(target)), an error in color coordinate is determined as theevaluation function as in an expression (13) below, and the steepestdescent method, the conjugate gradient method, or the genetic algorithmis desirably designed so as to minimize the evaluation function.Δxy=√{square root over ((x−x _(target))²+(y−y _(target))²)}  (13)

In order to improve efficiency in computation, design variables x[1],x[2], . . . , x[N] are determined in advance based on thedesign-of-experiments method, and parallel computation is desirablyperformed for combination of N design variables. Computation using agraphics processing unit (GPU), computation using cluster machines, orcomputation using multiple CPUs is employed for parallel computation.

(3.3.6 Example of Specific Optimization Loop)

A device shown in FIG. 23 was employed as the reference device, a frontcolor coordinate (x, y) was employed as desired characteristics, andoptimization computation was conducted so as to bring a target frontcolor coordinate closer to a green coordinate (0.30, 0.60) of sRGB.Thicknesses of a plurality of functional layers were employed as designvariables. The design-of-experiments method was adopted as theoptimization technique, and a plurality of levels were simultaneouslycomputed by carrying out parallel computation using multiple CPUs.

A difference Δxy (see an expression (14) below) from a target coordinateof a (x, y) color coordinate was employed as a desired characteristic,and Δxy=0 was set as a target value. Optimization computation wasaborted at N=256.Δxy=√{square root over ((x−0.3)²+(y−0.6)²)}  (14)

FIG. 31 shows a result of optimization computation. A level number N wasrenumbered in the descending order of magnitude of error. It can be seenin FIG. 31 that a combination x[256] of design variables is smallest indifference Δxy in the computation and it is a desirable combination ofdesign variables. FIG. 30 shows design variable x[256] as theoptimization result. It can be seen that the reference device and thedesign variables in FIG. 23 were varied. It can thus be seen thatoptimization for bringing desired characteristics closer to the targetvalues can be realized by deriving “relation between the designvariables and the desired characteristics.”

[4. Details of Method of Manufacturing Electroluminescent Device]

FIG. 32 shows a flow in application of the design method in theembodiment to the method of manufacturing an electroluminescent device.As described in [3. Details of Design Method], optimization loop R200 isonce run so as to output an optimal design. Then, an electroluminescentdevice is manufactured based on the optimal design variables.Thereafter, the manufactured electroluminescent device is inspected soas to measure and analyze current drive characteristics.

With the inspected electroluminescent device being defined as thereference device, optimization loop R200 is again run and feedback isgiven to the manufacturing process. By thus applying the design methodin the embodiment to the manufacturing method, an electroluminescentdevice having a desired characteristic value can be manufactured in astable manner.

EXAMPLES

[5.1 Single-Emission Light-Emitting Device]

In order to describe the effect of the present embodiment in furtherdetail, description will be given below with reference to analysis of anorganic electroluminescent device. Organic EL electroluminescent device100 to be analyzed has a structure shown in FIG. 22, in which ITO(having a thickness of 150 nm) was provided as transparent electrode 113on a glass substrate as transparent member 110 and first functionallayer 114 a, emissive layer 114 c (having a thickness of 20 nm), andsecond functional layer 114 e were provided through vacuum vapordeposition. Thereafter, an Ag film (having a thickness of 100 nm)serving as a reflective electrode was provided as second electrode 15. Agreen phosphorescent material having an emission peak wavelength of 520nm was employed for emissive layer 114 c. First functional layer 114 awas constituted of a hole injection layer, a hole transfer layer, and anelectron blocking layer (a total of 35 nm). Second functional layer 114e was constituted of a hole blocking layer, an electron transfer layer,and an electron injection layer (a total of x nm). Experiments andcomputation were compared with each other, with the total thickness fromthe hole blocking layer to the electron injection layer being varied.

FIG. 33 shows experimental results and results of comparison between theanalysis method in the background art and the analysis method in thepresent Example. FIG. 34 shows an error between experiments andanalysis. It can be seen that the present Example achieves accuratecomputation of a color chromaticity and external quantum efficiency inthe experiments. By using the analysis technique in the present Example,a more accurate color chromaticity and efficiency can be computed.Similar analysis is also applicable to analysis of a single-emissionelectroluminescent device shown in FIGS. 5 to 20.

[5.2 Transparent Light-Emitting Device]

The design method in the present embodiment is applicable toelectroluminescent devices 1F to 1H representing transparentlight-emitting devices shown in FIGS. 8 to 10. A quantity or a color oflight extracted to the outside from opposing sides can accurately beestimated by carrying out the method of designing an electroluminescentdevice in the present embodiment on a transparent light-emitting device.

[5.3 Construction Including Optical Buffer Layer]

The design method in the present embodiment is applicable toelectroluminescent devices 1I to 1J including the optical buffer layershown in FIGS. 11 and 12. A device with a desired color of whichefficiency is optimized can be designed by optimizing the design makinguse of an effect of improvement in luminous efficiency owing to themicrocavity effect of the optical multi-layer with the design method inthe present embodiment.

[5.4 Construction Including Optical Microstructure]

The design method in the present embodiment is applicable toelectroluminescent devices 1K to 1M including the optical microstructureshown in FIGS. 13 to 16. A light-emitting device high in luminousefficiency and less in deviation in emission intensity or color for eachangle can be realized by designing efficiency in extraction of waveguidemode light or plasmon light with the design method in the presentembodiment.

[5.5 Construction Including Second Optical Microstructure]

The design method in the present embodiment is applicable toelectroluminescent device 1O including the second optical microstructureshown in FIG. 17. A light-emitting device high in luminous efficiencyand less in deviation in emission intensity or color for each angle canbe realized by realizing design which allows efficient scattering ofsubstrate mode light.

[5.6 Electroluminescent Device]

Electroluminescent devices 1A to 1O designed by applying the designmethod in the present embodiment as shown in FIGS. 5 to 17 are useful asa surface-emitting light source which can highly efficiently exhibit adesired color. This is also applicable to electroluminescent devices 1Pto 1R shown in FIGS. 18 to 20.

The method of designing an electroluminescent device in the backgroundart computes an external light spectrum of an electroluminescent deviceresulting from current injection based on a photoluminescence spectrum,and disadvantageously, an actual external emission spectrum of theelectroluminescent device is different from the computed externalemission spectrum, and luminous efficiency or a color coordinate of theelectroluminescent device cannot accurately be computed.

In the method of designing an electroluminescent device in the presentembodiment, however, an external emission spectrum of an analyzed deviceis computed based on an external emission spectrum of a referencedevice, so that an electroluminescent device can be manufactured withaccurate efficiency or color coordinate being computed and desiredcharacteristics being optimized.

As set forth above, according to the embodiment, an external emissionspectrum output to the outside in a current injection state can moreaccurately be computed and a quantity or a color of light extracted tothe outside can accurately be estimated. By adopting the presentembodiment in a transparent light-emitting device, a quantity or a colorof light extracted to the outside on opposing sides can accurately beestimated. An electroluminescent device with a desired color of whichefficiency is optimized can be designed by optimizing the design makinguse of the effect of improvement in luminous efficiency owing to themicrocavity effect of the optical multi-layer with the technique in thepresent embodiment.

An electroluminescent device high in luminous efficiency and less indeviation in emission intensity or color for each angle can be realizedby designing efficiency in extraction of waveguide mode light or plasmonlight with the design method in the present embodiment. Anelectroluminescent device high in luminous efficiency and less indeviation in emission intensity or color for each angle can be realizedby designing efficiency in scattering of substrate mode light with thedesign method in the present embodiment. An electroluminescent devicedesigned with the design method in the present embodiment can highlyefficiently realize a desired color chromaticity.

Though a method of designing an electroluminescent device, anelectroluminescent device manufactured with the design method, and amethod of manufacturing an electroluminescent device with the designmethod in the present embodiment have been described above, it should beunderstood that the embodiment disclosed herein is illustrative andnon-restrictive in every respect. Therefore, the scope of the presentinvention is defined by the terms of the claims and is intended toinclude any modifications within the scope and meaning equivalent to theterms of the claims.

REFERENCE SIGNS LIST

1A, 1B, 1C, 1D 1E, 1F, 1G, 1H, 1I, 1J, 1K, 1L, 1N, 1M, 1O, 1P, 1Q, 1R(organic 41) electroluminescent device; 10 first transparent member(sealing member); 13 transparent electrode (first electrode); 13 a, 13 cconductive resin; 13 b small-thickness A1 (small-thickness metalelectrode); 14, 14A light-emitting layer; 14B, 14D charge generationlayer; 14C second light-emitting layer; 14E third light-emitting layer;14 a hole injection layer; 14 b hole transfer layer; 14 c emissivelayer; 14 d electron transfer layer; 14 e electron injection layer; 14 cemissive layer; 15 reflective electrode (second electrode); 16 supportsubstrate; 17 second transparent member; 19 second optical buffer layer;21 first optical microstructure; 21 a, 21 b light scattering layer; 21 csmooth layer; 21 d metal projection and recess structure; 21 etransparent conductive film; 23 third electrode (transparent electrode);24 fourth electrode (transparent electrode); 25 fifth electrode(transparent electrode); 26 sixth electrode (transparent electrode); 31second optical microstructure; 31 b transparent layer; 31 a lightscattering particle; 40 reflection member (Ag); 41, 42, 43, 44 opticalbuffer layer; 45 reflection member; 100 organic EL electroluminescentdevice; 110 transparent member; 113 transparent electrode; 114 a firstfunctional layer; 114 c emissive layer; 114 e second functional layer;and 115 second electrode.

The invention claimed is:
 1. A method of designing an electroluminescentdevice having an emissive layer between a first electrode and a secondelectrode, the first electrode and the second electrode beingtransparent electrodes, the emissive layer lying between a firstfunctional layer and a second functional layer, the electroluminescentdevice having a first transparent member on a side of the firstelectrode opposite to a side where the emissive layer is provided, themethod comprising: preparing a reference device including a constructionof the electroluminescent device and a desired analyzed device includinga construction of the electroluminescent device; performing quantumoptical analysis, electromagnetic analysis, and ray trace withthicknesses and complex relative permittivities of the first transparentmember, the first electrode, the first functional layer, the secondfunctional layer, the emissive layer, and the second electrode as wellas a position of a light-emitting point in the emissive layer and adistribution of light-emitting points in the emissive layer being usedas design variables; calculating a “ratio of light extractionefficiency” between the reference device and the analyzed device bycomputing efficiency of light extraction from the emissive layer intothe transparent member or air in both of the reference device and theanalyzed device; finding relation of the thickness and the complexrelative permittivity of each of the layers with the “ratio of lightextraction efficiency,” the layers forming the reference device and theanalyzed device; and obtaining the respective thicknesses and therespective complex relative permittivities of the first transparentmember, the first electrode, the first functional layer, the secondfunctional layer, the emissive layer, and the second electrode as thedesign variables, based on the relation and an electroluminescencespectrum in air or the first transparent member measured by feeding acurrent to the reference device.
 2. The method of designing anelectroluminescent device according to claim 1, wherein the secondelectrode is a transparent electrode, a second transparent member isprovided on a side of the second electrode opposite to a side where theemissive layer is provided, and a complex relative permittivity and athickness of the second transparent member are further included asdesign variables.
 3. The method of designing an electroluminescentdevice according to claim 2, wherein an optical buffer layer is furtherprovided between the second electrode and the first transparent memberand/or between the second electrode and the second transparent member,and the method further comprises designing a thickness, a complexrelative permittivity, and a structure constant of each film forming theoptical buffer film as design variables.
 4. The method of designing anelectroluminescent device according to claim 1, wherein a first opticalmicrostructure disturbing amplitude and a phase condition of light isfurther provided in any region between the transparent member and theemissive layer, and the method further comprises designing a structureconstant and a complex relative permittivity of the first opticalmicrostructure as design variables.
 5. The method of designing anelectroluminescent device according to claim 1, wherein a second opticalmicrostructure disturbing amplitude and a phase condition of light isprovided at an interface between the first transparent member andoutside, and a structure constant and a complex relative permittivity ofthe second optical microstructure are included as design variables. 6.An electroluminescent device designed with the method of designing anelectroluminescent device according to claim
 1. 7. A method ofmanufacturing an electroluminescent device comprising: inspecting anelectroluminescent device manufactured based on the design variablesobtained with the method of designing an electroluminescent deviceaccording to claim 1 and measuring and analyzing current drivecharacteristics; and obtaining the design variables with the method ofdesigning an electroluminescent device according to claim 1 with themeasured and analyzed electroluminescent device being defined as thereference device and manufacturing an electroluminescent device based onthe design variables.